1. Field of the Invention
The present invention relates to aqueous dispersions of polyvinylbutyrals having particular utility as coatings for metallic surfaces.
2. Description of the Prior Art
Various processes have been described which produce aqueous dispersions of polyvinylacetals. Thus, French Pat. No. 1,220,859 describes the production of polyvinylacetal dispersions by conducting the acetalization of the polyvinyl alcohol and the dispersion of the resultant acetal in a single operation. The reaction is accomplished at temperatures of between 70.degree. and 80.degree. C. in the presence of acid catalysts, particularly, alkylarylsulphonates containing one higher alkyl group, phenylcogasinic acid or phenylsinarolsulphonic acid.
The polyvinylacetals exhibit valuable properties as coatings. However, heretofore it has been necessary to use them in solution with organic solvents, and in the case of polyvinylbutyral, to incorporate large amounts of plasticizer in the solution. The organic solvent is required to maintain the stability of the dispersion while the plasticizer is required to increase adherence of the coating to the substrate. Thus, there remains a need in the art for an improved method of forming an aqueous dispersion of polyvinylbutyral which can be used as a coating without the inclusion of organic solvents or plasticizers.